1. Field of the Invention
The invention relates to an electrochemical sodium/sulfur storage cell of the type having anode and cathode spaces separated by a solid electrolyte and enclosed, at least in part, within a metallic housing.
Electrochemical storage cells of this type are very highly suitable as energy source. They are used to an increasing extent in the construction of high-temperature storage batteries for electric vehicles.
2. Description of the Related Art
A specific example of this type of cell is a rechargeable cell based on sodium and sulphur, and which has a solid beta-aluminum oxide electrolyte separating the anode space from the cathode space. An advantage of such storage cells, which should be emphasized, is that no electrochemical side reactions occur on charging and the current efficiency is therefore substantially about 100%. In storage cells of this type, the anode space is filled with sodium and is disposed within the solid electrolyte. The cathode space is located between the solid electrolyte and the metallic housing or container, which limits the storage cell externally. A light metal, in particular aluminum, is preferably used for the housing.
The reactants present in the storage cell and the reaction products formed on discharge of the storage cell are very corrosive. The metallic components of the housing which come into prolonged contact with the reactants therefore are subject to corrosive destruction in time. In order to alleviate this disadvantage, it has been proposed, in the journal "Thin Solid Films 83", page 417, to provide the inner surfaces of the metallic housing of such storage cells with a corrosion-protective coating.
The corrosion-protective material described is an alloy of chromium, nickel, cobalt and molybdenum.
German Published, Non-Prosecuted Application DE-OS No. 24 57 418 discloses an electrochemical storage cell on the inner surfaces of which a corrosion protective coating of graphite is applied.
U.S. Pat. No. 3,749,603 describes a metallic housing made from light metal having inner surfaces which are protected against corrosion by a molybdenum sulphide coating.
German Published, Non-Prosecuted Application DE-OS No. 31 17 381 discloses the production of an electrochemical storage cell, in which the inner surfaces of the metallic housing are coated with titanium, manganese, iron, cobalt or nickel.
Although the above-mentioned coatings are capable of improving the corrosion resistance of the housing in the short term, they have the disadvantage that the internal resistance of the storage cells increases very greatly with increasing age, due to formation of sulphide-containing or other non-conductive coatings on the inner wall of the housing. Furthermore, most of these materials used for corrosion protection are expensive, which significantly increases the overall cost of the storage cell.